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// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

package org.apache.doris.nereids.util;

import org.apache.doris.nereids.trees.expressions.Expression;
import org.apache.doris.nereids.trees.expressions.Slot;
import org.apache.doris.nereids.trees.expressions.SlotReference;
import org.apache.doris.nereids.trees.expressions.visitor.DefaultExpressionVisitor;

import com.google.common.collect.Sets;

import java.util.Collection;
import java.util.Set;

/**
 * Extracts the SlotReference contained in the expression.
 */
public class SlotExtractor {
    private static final DefaultExpressionVisitor<Void, Set<Slot>> SLOT_COLLECTOR
            = new DefaultExpressionVisitor<Void, Set<Slot>>() {
                @Override
                public Void visitSlotReference(SlotReference slotReference, Set<Slot> context) {
                    context.add(slotReference);
                    return null;
                }
            };

    /**
     * extract slot reference.
     */
    public static Set<Slot> extractSlot(Collection<Expression> expressions) {
        Set<Slot> slots = Sets.newHashSet();
        for (Expression expression : expressions) {
            extractSlot(expression, slots);
        }
        return slots;
    }

    /**
     * extract slot reference.
     */
    public static Set<Slot> extractSlot(Expression... expressions) {
        Set<Slot> slots = Sets.newHashSet();
        for (Expression expression : expressions) {
            extractSlot(expression, slots);
        }
        return slots;
    }

    private static void extractSlot(Expression expression, Set<Slot> slots) {
        expression.accept(SLOT_COLLECTOR, slots);
    }
}
